Creates WindowToken for WindowContext

...  until it adds the first view

In R, we create WindowToken for every WindowContext creation.
In S, we only create WindowToken for the WindowContext which adding
a view.
This CL also provide the ability to attach an existing WindowToken
by overriding WindowManager.LayoutParams.mToken, and remove the
WindowContext created WindowToken after WindowContext destruction.

Bug: 159767464
Bug: 153369119
Test: atest WindowTokenTests WindowContextListenerControllerTests
Change-Id: Iefe0315461b452a84cecbff2d08ee04c1f34051d